Field of the Invention
The present invention relates to a wire electrical discharge machine that performs electrical discharge machining on a workpiece in a working fluid.
Description of the Related Art:
Recently, materials containing magnesium have been widely used in automotive application (automobiles), IT equipment and the like in order to reduce the weight of parts. For this reason, the wire electrical discharge machine in which electric current is flowed through a wire electrode to perform electrical discharge machining has become required to deal with workpieces containing magnesium. Though the wire electrical discharge machine can machine objects containing magnesium easily, the machining process entails safety problems of machined swarf (chips) produced by machining.
The machined chips containing magnesium are very fine and have high chemical reactivity, but they, forming a passive film in the dielectric working fluid, are unlikely to react with air. Nevertheless, once water or fluid runs out around the machined swarf containing magnesium, they will react with oxygen (O2) and carbon dioxide (CO2) in the air and oxidize. When magnesium oxidizes forming magnesium oxide, this reaction gives off intense heat (intense heat of reaction). The reaction formula of formation of magnesium oxide is as follows:2Mg+CO2→2MgO+C (generation of intense heat of reaction)2Mg+O2→2MgO (generation of intense heat of reaction)
The amount of machined swarf (magnesium) adhering to the tanks (pans) or piping of the wire electrical discharge machine will hardly cause problems involving heat of reaction. However, since the filter for collecting the machined swarf contains a large amount of magnesium therein, this causes heat reaction problem. For example, when water or fluid in the filter is taken out for such a work as replacing filters, a large amount of magnesium in the filter is oxidized so that intensive reaction heat is generated, which may lead to ignition of the filter.
To deal with this problem, Japanese Laid-Open Patent Publication No. 2005-008480 discloses a method whereby fine magnesium particles are dissolved in an acid solution, an alkaline solution is added to form magnesium hydroxide, which is then flocculated and sedimented with a flocculating agent and further dehydrated.